I just bought 1970 442 and replaced the battery and alternator. The GEN light is still on. Can anyone direct me to what the issue may be?

 

You will need two items to trace down this problem .
1. A small digital volt - ohm meter .
2. A copy of the 1970 Oldsmobile Chassis Manual . It contains a wiring diagram .
Check all the connections and wiring for disconnected or shorted wiring .
Start the engine and check the voltage across the battery . It should be between 13.5 volts and 14.5 volts .
If it is , then the problem is in the voltage regulator or the wiring .
If you have less than 13 volts , then the problem is either the alternator or regulator .
You can test the alternator by " full fielding " it , Remove the small square connection with two wires on the back of the alternator .
One terminal will be marked " F ". Make a jumper wire to connect to this terminal about four feet long .
Then start the engine and hook up the voltmeter to the battery .
Touch the jumper on the positive battery post for a second or two and observe the volt meter .
You should have 14 or more volts . If you do , then the alternator is good .
The Olds manual will detail the test and repair procedures better than I can .Good luck .

 

Did you have the new alternator tested at the parts store before you left with it? They can be bad out of the box.

Next- is it charging the battery? If you have a voltmeter, check voltage at the alternator output post (thick red wire, may have a red or black plastic cap on it) with engine running above idle rpm. Working properly should be 14 volts or so. If not, alternator problem.

Then check voltage at the battery positive terminal under same conditions. Should be the same voltage as at alternator output post. If not, bad wiring. First thing to look at would be the fusible link in the main wires at the electrical junction post on the fenderwell.

If you don't have one, a factory 1970 Oldsmobile Chassis Service Manual is a good investment. Covers almost all aspects of repairing your car. A 1970 Motor's, Chilton's or Glenn's Professional Trades Edition Shop Manual is also a worthwhile investment as those often have detailed unit and component troubleshooting procedures. Usually available on Ebay or someone here may have one. The 1970 factory CSM has been reproduced, but find an original if possible. You and your mechanic will both benefit.

Stop to think- even if a mechanic is 50 years old odds are he's never done much of anything on an older car, and younger ones have rarely encountered a car that can't be diagnosed with a computer. And that's where Olds dogs like us come in!

 

Post a picture of your alternator, particularly the wire connections and plug. Also post a picture of the firewall between the brake booster and the center of the car.

Sounds like this problem was there when you bought the car, yes?

Does the light go out if you unplug the alternator?

Good luck!!!

 

Agreed. If this car's had one of those damned one-wire alternators put on, that creates a new diagnosis that I will be first to tell you I don't know diddly-squat about.

 

Are you still using an external voltage regulator? It could be a bad regulator. Or if the previous owner converted to an internal voltage regulator, they might have not jumper-ed the old voltage regulator wiring leaving the light not to work properly.

 

Good point but if this is a real 442 it would have had internal regulator charging system from factory. Can't remember offhand what year Olds switched to IR on all carlines, 70 or 71.

That's the problem with having older cars. You never know what some previous owner or shop has done to it, often with no documentation except a poorly spliced wire. On another thread a '70 owner has a car with both NightWatch and Rallye Pac- which the factory specs book and car order form clearly state cannot be had together. But sometime in the last 50 years, the car has had both installed.